This invention is generally directed to improved toner compositions, and developer compositions containing styrene butadiene copolymer resins. More specifically, the present invention is directed to improved toner compositions comprised of a blend of styrene butadiene copolymer resin particles, and a plasticizer composition. The resulting toner compositions, which have stable electrical properties, desirable glass transition temperatures, desirable melt viscosities, and excellent mechanical properties are suitable for selection in developing images in electrostatic imaging systems, especially those systems wherein the imaging member is charged negatively.
The development of electrostatic latent images, particularly positively charged images, with toner compositions, comprised of a blend of toner resin particles and pigment particles is well known. Generally, in these systems, negatively charged toner particles are selected for the development of the positively charged electrostatic latent images. Recently, however, there has been disclosed positively charged toner compositions containing charge enhancing additives for the purpose of imparting positive charges to the toner resin particles. These positively charged toner compositions are particularly useful for causing the development of negatively charged electrostatic latent images formed on layered organic photoresponsive imaging members. Examples of positively charged toner compositions useful for causing the development of negatively charged electrostatic latent images, are disclosed in U.S. Pat. No. 4,298,672. This patent describes as charge enhancing additives for toner compositions alkyl pyridinium halides, including cetyl pyridinium chloride. Additionally, there is disclosed in U.S. Pat. No. 4,338,390 the use of sulfate and sulfonate compositions, such as stearyl dimethyl phenethyl ammonium para-toluene sulfonate, as charge enhancing additives. In accordance with the disclosure of this Patent, from about 0.1 percent to about 10 percent by weight of the sulfate or sulfonate charge enhancing additive is incorporated into the toner composition, for the purpose of imparting positive charges to the toner resin particles.
Illustrative examples of toner resin particles include numerous known resin compositions, such as styrene butadiene copolymers. For example, there is disclosed in U.S. Pat. No. 3,326,848 a toner composition containing as resin particles a styrene butadiene copolymer, and the use of this composition for developing positively charged latent electrostatic images. Also, there is disclosed in U.S. Pat. No. 3,960,737 a liquid developer composition containing a mixture of a styrene butadiene copolymer and an acrylate. Moreover, in U.S. Pat. No. 3,766,072 there is described a developer composition containing at least two types of particles, one of which is the specific styrene butadiene copolymer resin, designated Pliolite S5D. Additionally, there is disclosed in a copending application the selection of certain specific styrene butadiene resins for incorporation into toner compositions, which compositions can subsequently be used for developing negatively charged electrostatic images. The toner compositions disclosed in this application can contain charge enhancing additives, for the purpose of imparting a positive charge to the styrene butadiene resin particles.
While some of the known styrene butadiene toner compositions may exhibit acceptable fusing latitudes, desirable melt fixing temperatures, and appropriate glass transition temperatures for certain uses, these compositions usually do not simultaneously possess such properties in combination. Also several of the known toner compositions cannot achieve excellent triboelectric admix charging behavior, which is essential for the development of high quality images of excellent resolution. Furthermore, while several of the toner compositions involved may possess acceptable low minimum fix temperatures, their molecular weight may be too low to permit them to be easily formulated into toner compositions, or to provide toner compositions with a sufficient fusing latitude response. Additionally, these compositions usually do not exhibit the appropriate triboelectric charging behavior which would render them suitable for the development of images wherein the photoreceptor is charged negatively. Moreover, these toner compositions may possess the appropriate triboelectric charging characteristics, however, the melt fusing temperature, and fusing latitude for such compositions are not of the desired values causing image deterioration when these toners are used in an imaging system.
Accordingly, there continues to be a need for improved toner compositions and developer compositions, containing styrene butadiene resin particles. There also continues to be a need for toner compositions containing styrene butadiene resins, which have specific parameters associated therewith including a molecular weight of a specific range, a fusing temperature latitude of at least about 60 degrees Fahrenheit, a glass transition temperature within a certain range, and acceptable triboelectric charging characteristics. There also continues to be a need for toner polymer compositions which are capable of improved toner processing response, enabling a significant reduction in the toner unit manufacturing costs, as a result of lower toner micronizability parameters.